About 1/3 of a century ago, I repainted my 16' ski boat with automotive lacquer in two-tone color. I mixed a fine glitter into both colors. The glitter made the finish feel like 140 grit sandpaper. After a full cure (4+ days), I did a heavy coat of clear urethane over the whole thing. The clear urethane (PPG "Delthane" as I recall) did a great job flowing and covering the roughness of the lacquer/glitter. As a matter of fact, when I saw it the next morning, I thought it was still wet, but it was dry. I had that boat for 20 more years with hardly any fading or cracking. (I did keep it covered most of the time)
Clear Urethane or PolyUrethane over lacquer or enamel is an interesting option for multicolor paint jobs including air-brushed artwork, as your topcoat (clear) would not have any masking lines.
In more modern times, I hear of people using IMRON (a polyurethane?) on boats and airplanes with great success. Usually this is with color coats and no clear coat.
Here is an interesting discussion on the Polyurethane / Acrylic Urethane / etc terminology:
http://www.hotrodders.com/forum/enamel-vs-urethane-vs-polyurethane-43949.htmlAs the others have said, it would be interesting to see pictures of what you have now. There may be suggestions on repairing your gelcoat. Painting a whole boat is no small task... your 20' boat would be about like painting 2 to 3 cars.
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings